Minimizing interference to non-associated users

ABSTRACT

A method for reducing interference to wireless communication devices is described. It is determined that a base station is deployed with a first coverage area that overlaps a second coverage area of a femto access point. The base station uses a first carrier for wireless communications. The femto access point uses a second carrier for wireless communications. Transmissions by the femto access point interfere with transmissions by the base station. An amount of radio frequency (RF) leakage experienced by wireless communication devices communicating with the base station is estimated. Interference experienced by the wireless communication devices is minimized.

RELATED APPLICATIONS

This application is related to and claims priority from U.S. ProvisionalPatent Application Ser. No. 61/179,455, filed May 19, 2009, for“Femtocell Carrier and Power Adjustment to Minimize Interference toNon-Associated Users.”

TECHNICAL FIELD

The present disclosure relates generally to wireless communicationsystems. More specifically, the present disclosure relates to systemsand methods for minimizing interference to non-associated users.

BACKGROUND

Wireless communication systems have become an important means by whichmany people worldwide have come to communicate. A wireless communicationsystem may provide communication for a number of mobile stations, eachof which may be serviced by a base station.

It may be beneficial to use localized base stations that provide serviceto a select group of mobile stations. These localized base stations mayuse less power and have smaller coverage areas than normal basestations. The localized base stations may then provide a mobile stationwith active voice/data access. As localized base stations continue toimprove, more localized base stations will become prevalent.

Examples of localized base stations include femtocells and picocells.Localized base stations may be referred to as femto access pointswithout loss of generality. These localized base stations may becontrolled by a user. For example, a localized base station may bepurchased by an end user and placed in their home or office to increasewireless coverage. A localized base station may also be controlled by aservice provider. For example, a service provider may place a localizedbase station in a public area with high traffic.

As a mobile station approaches a localized base station, the mobilestation may detect the localized base station and attempt to access itby sending a registration request. The localized base station may thendetermine whether to allow access to this mobile station for differentservices such as a voice/data connection with the mobile station. Mobilestations that are near these localized base stations but not part of theselect group may receive strong interference from the localized basestations. This strong interference, in some instances, may prevent amobile station from obtaining access to a normal base station. As such,benefits may be realized by minimizing the interference of localizedbase stations on mobile stations.

SUMMARY

A method for reducing interference to wireless communication devices, isdescribed. It is determined that a base station is deployed with a firstcoverage area that overlaps a second coverage area of a femto accesspoint. The base station uses a first carrier for wireless communicationsand the femto access point uses a second carrier for wirelesscommunications. Transmissions by the femto access point interfere withtransmissions by the base station. An amount of radio frequency (RF)leakage experienced by wireless communication devices communicating withthe base station is estimated. Interference experienced by the wirelesscommunication devices is minimized.

The method may be performed by the femto access point or by a corenetwork apparatus. The base station may be a femto access point or amacro base station. Determining that a base station is deployed mayinclude monitoring a downlink signal strength on the first carrier.Minimizing the interference experienced by the wireless communicationdevices may include adjusting a transmit power of the femto accesspoint. A third carrier may be determined. Minimizing the interferenceexperienced by the wireless communication devices may include switchingthe femto access point to communicating using the third carrier. Thethird carrier may have fewer base station and femto access pointdeployments than the second carrier or the third carrier may have nobase station or femto access point deployments. The first carrier andthe second carrier may be the same carrier. The first carrier and thesecond carrier may also be adjacent.

The method may be performed by a core network. Adjusting a transmitpower of the femto access point may include sending an adjusted transmitpower to the femto access point. Switching the femto access point tocommunicating using the third carrier may include sending the thirdcarrier to the femto access point. Estimating the amount of RF leakagemay be performed using a current transmit power of the femto accesspoint, the second carrier used by the femto access point, the firstcarrier used by the base station and an adjacent channel interferenceratio (ACIR). Adjusting a transmit power of the femto access point maytake into account a proximity of the femto access point to the basestation.

A wireless device configured for reducing interference to wirelesscommunication devices is also described. The wireless device includes aprocessor, memory in electronic communication with the processor andinstructions stored in the memory. The instructions are executable bythe processor to determine that a base station is deployed with a firstcoverage area that overlaps a second coverage area of a femto accesspoint. The base station uses a first carrier for wireless communicationsand the femto access point uses a second carrier for wirelesscommunications. Transmissions by the femto access point interfere withtransmissions by the base station. The instructions are also executableto estimate an amount of radio frequency (RF) leakage experienced bywireless communication devices communicating with the base station. Theinstructions are further executable to minimize interference experiencedby the wireless communication devices.

A wireless device configured for reducing interference to wirelesscommunication devices is described. The wireless device includes meansfor determining that a base station is deployed with a first coveragearea that overlaps a second coverage area of a femto access point. Thebase station uses a first carrier for wireless communications and thefemto access point uses a second carrier for wireless communications.Transmissions by the femto access point interfere with transmissions bythe base station. The wireless device also includes means for estimatingan amount of radio frequency (RF) leakage experienced by wirelesscommunication devices communicating with the base station. The wirelessdevice further includes means for minimizing interference experienced bythe wireless communication devices.

A computer-program product for reducing interference to wirelesscommunication devices is also described. The computer-program productincludes a computer-readable medium having instructions thereon. Theinstructions include code for determining that a base station isdeployed with a first coverage area that overlaps a second coverage areaof a femto access point. The base station uses a first carrier forwireless communications and the femto access point uses a second carrierfor wireless communications. Transmissions by the femto access pointinterfere with transmissions by the base station. The instructions alsoinclude code for estimating an amount of radio frequency (RF) leakageexperienced by wireless communication devices communicating with thebase station. The instructions further include code for minimizinginterference experienced by the wireless communication devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wireless communication system with multiple wirelessdevices;

FIG. 2 is a block diagram of a vicinity deployment module;

FIG. 3 is a flow diagram of a method for minimizing the interference towireless communication devices near a femto access point;

FIG. 3A illustrates means-plus-function blocks corresponding to themethod of FIG. 3;

FIG. 4 is a flow diagram of another method for minimizing theinterference to wireless communication devices near a femto accesspoint;

FIG. 4A illustrates means-plus-function blocks corresponding to themethod of FIG. 4;

FIG. 5 is a timing diagram illustrating a mobile sensing approach tominimizing interference to wireless communication devices near a femtoaccess point;

FIG. 6 illustrates the transmission of a handoff request from a wirelesscommunication device to a core network;

FIG. 7 is a flow diagram of a method for interference management;

FIG. 7A illustrates means-plus-function blocks corresponding to themethod of FIG. 7;

FIG. 8 is a flow diagram of a method for mobile sensing;

FIG. 8A illustrates means-plus-function blocks corresponding to themethod of FIG. 8;

FIG. 9 is a flow diagram of another method for interference management;

FIG. 9A illustrates means-plus-function blocks corresponding to themethod of FIG. 9;

FIG. 10 illustrates certain components that may be included within afemto access point;

FIG. 11 illustrates certain components that may be included within acore network apparatus;

FIG. 12 illustrates two wireless devices in a multiple-in andmultiple-out (MIMO) system;

FIG. 13 illustrates a wireless communication system, configured tosupport a number of users, in which the teachings herein may beimplemented;

FIG. 14 illustrates an exemplary communication system where one or morefemto nodes are deployed within a network environment; and

FIG. 15 illustrates an example of a coverage map where several trackingareas (or routing areas or location areas) are defined.

DETAILED DESCRIPTION

FIG. 1 shows a wireless communication system 100 with multiple wirelessdevices. Wireless communication systems 100 are widely deployed toprovide various types of communication content such as voice, data, andso on. These systems may be multiple-access systems capable ofsupporting communication with multiple users by sharing the availablesystem resources (e.g., bandwidth and transmit power). A wireless devicemay be a base station 102, a wireless communication device 104 or afemto access point 106. A core network 114 is also illustrated in FIG.1.

The core network 114 is the central part of a telecommunications networkthat provides various services to customers that are connected to thecore network 114. The core network 114 may be a single entity ormultiple entities that facilitate wireless communication betweenmultiple wireless communication devices 104. The core network 114 mayinclude multiple processors in one or more locations. The core network114 may be an apparatus or group of apparatuses. One of the mainfunctions of the core network 114 is to route calls across the publicswitched telephone network (PTSN). The core network 114 may provide apath for the exchange of information between different sub-networks. Thecore network 114 may include switches and routers.

A base station 102 is a station that communicates with one or morewireless communication devices 104. A base station 102 may also bereferred to as, and may include some or all of the functionality of, anaccess point, a broadcast transmitter, a NodeB, an evolved NodeB, etc.The term “base station” will be used herein. Each base station 102provides communication coverage for a particular geographic area. A basestation 102 may provide communication coverage for one or more wirelesscommunication devices 104. The term “cell” can refer to a base station102 and/or its coverage area depending on the context in which the termis used.

A base station 102 may be referred to as an evolved NodeB (eNB). Asemi-autonomous base station may be referred to as a home evolved NodeB(HeNB). An HeNB may thus be one example of an eNB. The HeNB and/or thecoverage area of an HeNB may be referred to as a femtocell, a picocell,an HeNB cell, a femto access point 106 or a closed subscriber group(CSG) cell. Femto access point 106 is used herein. Femto access points106 are low-power base stations that extend the range of conventionalwide area network base stations. Femto access points 106 provide voiceand high-speed data service inside homes and offices for wirelesscommunication devices 104 supporting cellular radio communicationtechniques.

Access to a femto access point 106 depends on the kind of access controlthat the femto access point 106 uses. With open access, any wirelesscommunication device 104 can access and receive service from a femtoaccess point 106. With closed subscriber group (CSG) or restrictedaccess, only members of the CSG are allowed to access and receiveservice from a femto access point 106. A wireless communication device104 that is not part of the closed subscriber group (CSG) is thus notable to be associated with the femto access point 106.

Communications in a wireless communication system 100 (e.g., amultiple-access system) may be achieved through transmissions over awireless link. Such a communication link may be established via asingle-input and single-output (SISO), multiple-input and single-output(MISO), or a multiple-input and multiple-output (MIMO) system. A MIMOsystem includes transmitter(s) and receiver(s) equipped, respectively,with multiple (NT) transmit antennas and multiple (NR) receive antennasfor data transmission. SISO and MISO systems are particular instances ofa MIMO system. The MIMO system can provide improved performance (e.g.,higher throughput, greater capacity or improved reliability) if theadditional dimensionalities created by the multiple transmit and receiveantennas are utilized.

The teachings herein may be incorporated into various types ofcommunication systems and/or system components. In some aspects, theteachings herein may be employed in a multiple-access system capable ofsupporting communication with multiple users by sharing the availablesystem resources (e.g., by specifying one or more of bandwidth, transmitpower, coding, interleaving, and so on). For example, the teachingsherein may be applied to any one or combinations of the followingtechnologies: Code Division Multiple Access (CDMA) systems,Multiple-Carrier CDMA (MCCDMA), Wideband CDMA (W-CDMA), High-SpeedPacket Access (HSPA, HSPA+) systems, Time Division Multiple Access(TDMA) systems, Frequency Division Multiple Access (FDMA) systems,Single-Carrier FDMA (SC-FDMA) systems, Orthogonal Frequency DivisionMultiple Access (OFDMA) systems or other multiple access techniques.

A wireless communication system employing the teachings herein may bedesigned to implement one or more standards, such as IS-95, cdma2000,IS-856, W-CDMA, time division synchronous code division multiple access(TD-SCDMA) and other standards. A CDMA network may implement a radiotechnology such as Universal Terrestrial Radio Access (UTRA), cdma2000or some other technology. UTRA includes W-CDMA and Low Chip Rate (LCR).The cdma2000 technology covers IS-2000, IS-95 and IS-856 standards. ATDMA network may implement a radio technology such as Global System forMobile Communications (GSM). An OFDMA network may implement a radiotechnology such as Evolved UTRA (E-UTRA), IEEE 802.11, IEEE 802.16, IEEE802.20, Flash-OFDM®, etc. UTRA, E-UTRA and GSM are part of UniversalMobile Telecommunication System (UMTS). The teachings herein may beimplemented in a Third Generation Partnership Project (3GPP) Long TermEvolution (LTE) system, an Ultra-Mobile Broadband (UMB) system and othertypes of systems. LTE is a release of UMTS that uses E-UTRA. Althoughcertain aspects of the disclosure may be described using 3GPPterminology, it is to be understood that the teachings herein may beapplied to 3GPP (Re199, Re15, Re16, Re17) technology, as well as 3GPP2(IxRTT, 1xEV-DO RelO, RevA, RevB) technology and other technologies. Forclarity, certain aspects of the techniques are described below forcdma2000, and cdma2000 terminology is used in much of the descriptionbelow.

Low power base stations such as home evolved NodeBs (HeNB), picocellsand femtocells are used in addition to the normal base stations (anormal base station is referred to herein as a macro base station 102).A picocell may refer to a base station controlled by the networkoperator that operates on a much smaller scale than a macro base station102. A femtocell may refer to a base station controlled by a consumerthat operates on a much smaller scale than a macro base station 102. Afemtocell may provide service to a closed subscriber group (CSG). Theselow power base stations are referred to herein as femto access points106. A femto access point 106 may communicate with the core network 114via a DSL router (not shown) or a cable modem (not shown).

The macro base station 102 may communicate with one or more wirelesscommunication devices 104. A wireless communication device 104 may alsobe referred to as, and may include some or all of the functionality of,a terminal, an access terminal, a user equipment (UE), a subscriberunit, a station, etc. A wireless communication device 104 may be acellular phone, a personal digital assistant (PDA), a wireless device, awireless modem, a handheld device, a laptop computer, etc. A wirelesscommunication device 104 may communicate with zero, one or multiple basestations 102 on the downlink 110 and/or uplink 108 at any given moment.The downlink 110 (or forward link) refers to the communication link froma base station (such as a macro base station 102 or a femto access point106) to a wireless communication device 104 and the uplink 108 (orreverse link) refers to the communication link from a wirelesscommunication device 104 to a base station.

A wireless communication device 104 may be part of a closed subscribergroup (CSG). A femto access point 106 may restrict access to the femtoaccess point 106 to wireless communication devices 104 that are part ofthe closed subscriber group (CSG). The wireless communication device 104of FIG. 1 may not be part of the closed subscriber group (CSG)corresponding to the femto access point 106. The wireless communicationdevice 104 may instead communicate with a macro base station 102 via anuplink 108 and downlink 110. However, the wireless communication device104 may be located within the coverage region of the femto access point106. Thus, the femto access point 106 may receive uplink pilot signals112 from the wireless communication device 104.

Due to the unplanned deployment of femto access points 106, a femtoaccess point 106 can cause downlink interference 120 to a wirelesscommunication device 104 communicating with a macro base station 102 orother femto access point when the coverage area of the femto accesspoint 106 overlaps the coverage area of the macro base station 102 orother femto access point. For example, a femto access point 106installed near a window of a residence can cause significant downlinkinterference 120 to a wireless communication device 104 serviced by amacro base station 102. Similarly, in a multiple resident apartmentbuilding, a femto access point 106 installed near a wall separating tworesidences can cause significant interference to wireless communicationdevices 104 operated by the neighbors.

Although this problem is most severe in co-channel (i.e., singlecarrier) femto access point 106 and macro base station 102 deployments,it can still pose a problem when the femto access point 106 and thenearby wireless communication device 104 are on different carriers(either adjacent or further separated) due to radio frequency (RF)leakage from the femto access point 106. In one configuration the femtoaccess point 106 and the nearby wireless communication device 104 mayuse the same carrier. To reduce/minimize the downlink interference 120,the femto access point 106 may reduce the downlink transmit power orswitch to a different carrier.

The femto access point 106 may include a vicinity deployment module 118a. The vicinity deployment module 118 a may estimate the amount of RFleakage (i.e., downlink interference 120) the femto access point 106creates for nearby wireless communication devices 104. The vicinitydeployment module 118 a may then adjust the transmit power of the femtoaccess point 106. Alternatively, the vicinity deployment module 118 amay switch the femto access point 106 to a different carrier. When thereare no nearby wireless communication devices 104, the femto access point106 may increase the transmit power.

In one configuration, the core network 114 may include a vicinitydeployment module 118 b. The vicinity deployment module 118 b on thecore network 114 may perform a similar function as the vicinitydeployment module 118 a on the femto access point 106 except that thevicinity deployment module 118 b on the core network 114 may receivenetwork information from the femto access point 106, make decisions forthe femto access point 106 and send instructions to the femto accesspoint 106. Vicinity deployment modules 118 are discussed in furtherdetail below in relation to FIG. 2.

The core network 114 may also include a mobile sensing module 122. Themobile sensing module 122 may sense requests for active user hand-insupport by wireless communication devices 104. In other words, themobile sensing module 122 may detect requests by a wirelesscommunication device 104 to attempt a hand-off from the macro basestation 102 to the femto access point 106. The mobile sensing module 122may then instruct the femto access point 106 to adjust transmit powerand/or switch to a different carrier to reduce the interferenceexperienced by the wireless communication device 104.

The femto access point 106 may include an uplink measurement module 124.The uplink measurement module 124 may measure the signal strength ofreceived uplink pilot signals 112 from a wireless communication device104 that has requested a hand-off to a hand-in target such as the femtoaccess point 106. Hand-in targets are discussed in further detail belowin relation to FIG. 5.

The femto access point 106 may also include an interference managementmodule 125. The interference management module 125 may adjust thetransmit power of the femto access point 106 and/or switch the femtoaccess point 106 to a different carrier when instructions from the corenetwork 114 indicate so or when the femto access point 106 hasautonomously decided to do so. The interference management module 125may limit the coverage holes created by the femto access point 106 forwireless communication devices 104 that are not part of the closedsubscriber group (CSG) associated with the femto access point 106.

In one configuration, the interference management module 125 may receiveinstructions from the core network 114 on when to adjust the transmitpower. The interference management module 125 may then determine thetransmit power adjustments to be made. In another configuration, theinterference management module 125 may receive instructions from thecore network 114 that indicate what transmit power adjustments should bemade. The interference management module 125 may also receiveinstructions from the core network 114 about when to switch to anothercarrier. The interference management module 125 may then determine whichcarrier to switch to. In one configuration, the instructions from thecore network 114 may indicate which carrier the femto access point 106is to switch to.

In one configuration, the core network 114 may include an uppermanagement server 116. The upper management server 116 may allow thecore network 114 to manage one or more femto access points 106. Forexample, the upper management server 116 may allow the vicinitydeployment module 118 b on the core network 114 to control the transmitpower and/or carrier selection of the femto access point 106. The uppermanagement server 116 may be a femto convergence server (FCS).

FIG. 2 is a block diagram of a vicinity deployment module 218. Thevicinity deployment module 218 of FIG. 2 may be one configuration ofeither the vicinity deployment module 118 a on the femto access point106 or the vicinity deployment module 118 b on the core network 114. Thevicinity deployment module 218 may receive nearby deployment information226. Received nearby deployment information 226 may indicate that amacro base station 102 (or other femto access point) is deployed with acoverage area that overlaps the coverage area of the femto access point106. Received nearby deployment information 226 may be received from afemto access point 106 (if the vicinity deployment module 218 is on acore network 114), received from a core network 114 or received from amacro base station 102 (via the core network 114 if the vicinitydeployment module 218 is on a femto access point 106).

The received nearby deployment information 226 may indicate that awireless communication device 104 not part of the closed subscribergroup (CSG) associated with the femto access point 106 is nearby thefemto access point 106 and is trying to handoff to the femto accesspoint 106. In one configuration, the received nearby deploymentinformation 226 may indicate that the wireless communication device 104is close enough to the femto access point 106 that interferencemanagement is necessary.

The vicinity deployment module 218 may receive measured signal strengths228 of detected background signals. For example, if the vicinitydeployment module 218 is on a femto access point 106, the femto accesspoint 106 may measure the signal strength of downlink signals 110 (suchas a background signal on an adjacent or further separated frequencyfrom the downlink signals used by the femto access point 106) sent bythe macro base station 102. The femto access point 106 may then providethe measured signal strengths 228 to the vicinity deployment module 218.As another example, if the vicinity deployment module 218 is on the corenetwork 114, the measured signal strengths 228 of downlink signals 110received by the femto access point 106 from the macro base station 102may be forwarded to the core network 114 and provided to the vicinitydeployment module 218 on the core network 114.

The vicinity deployment module 218 may include a deployment informationmodule 230. The deployment information module 230 may obtain nearbydeployment information 232 from the measured signal strengths 228 ofdetected background signals. Similar to received nearby deploymentinformation 226, the obtained nearby deployment information 232 mayindicate that a macro base station 102 (or other femto access point) isdeployed with a coverage area overlapping the coverage area of the femtoaccess point 106. Both the received nearby deployment information 226and the derived nearby deployment information 232 may includeinformation about the current carrier of the macro base station 102 (orother femto access point).

The vicinity deployment module 218 may also include carrier information234. The carrier information 234 may include the current carrier of thefemto access point 106. The carrier information 234 may also includepotential carriers that the femto access point 106 may switch to ifnecessary. In one configuration, the carrier information 234 may includethe channel deployments of adjacent (or further separated) carriers. Forexample, the carrier information 234 may indicate which carriers nearthe current carrier are used by nearby wireless communication devices104 with the potential for interference.

The vicinity deployment module 218 may include the current transmitpower 236 of the femto access point 106. The vicinity deployment module218 may also include an adjacent channel interference ratio (ACIR) 238.The adjacent channel interference ratio (ACIR) 238 is the ratio of thepower on the desired channel to the interference power created for theadjacent channels. The adjacent channel interference ratio (ACIR) 238may thus represent the amount of interference that will be caused toadjacent channels by the current transmit power 236 of the femto accesspoint 106. The adjacent channel interference ratio (ACIR) 238 is afunction of the transmitter and receiver design of the femto accesspoint 106 and the wireless communication device 104. The adjacentchannel interference ratio (ACIR) 238 may be known to or estimated bythe vicinity deployment module 218.

In one configuration, the vicinity deployment module 218 may determinethat the femto access point 106 should switch to a different carrier.The vicinity deployment module 218 may then output the determineddifferent carrier 242 (i.e., an indication of which carrier to switchto). In another configuration, the vicinity deployment module 218 maydetermine that the femto access point 106 should adjust the transmitpower. The vicinity deployment module 218 may then output the adjustedtransmit power 244 to be used by the femto access point 106. If thevicinity deployment module 218 is on the core network 114, thedetermined different carrier 242 and/or adjusted transmit power 244 maybe sent to the femto access point 106.

FIG. 3 is a flow diagram of a method 300 for minimizing the interferenceto wireless communication devices 104 near a femto access point 106. Themethod 300 may be performed by a vicinity deployment module 218. Thevicinity deployment module 218 may be located on a femto access point106 or on the core network 114. The vicinity deployment module 218 maydetermine 302 that a macro base station 102 (or other femto accesspoint) is deployed on an adjacent (or further separated) frequency witha coverage area that overlaps the coverage area of the femto accesspoint 106. In other words, the vicinity deployment module 218 maydetermine that a macro base station 102 (or other femto access point)with a coverage area overlapping the coverage area of the femto accesspoint 106 is using a carrier that is close to the carrier used by thefemto access point 106. A carrier that is close/adjacent to anothercarrier does not have to be immediately adjacent to the other carrier.Instead, a carrier that is close/adjacent to another carrier may bemultiple carriers away in either direction (i.e., above or below thefrequency of the carrier).

The vicinity deployment module 218 may estimate 304 the amount of radiofrequency (RF) leakage for wireless communication devices 104communicating with the macro base station 102 (or other femto accesspoint) on the adjacent (or further separated) frequency. The amount ofradio frequency (RF) leakage may depend on the current transmit power236 of the femto access point 106, the current carrier of the femtoaccess point 106, the carrier used by the macro base station 102 (orother femto access point) and the adjacent channel interference ratio(ACIR) 238. For example, an interference threshold limiting the amountof interference created on nearby wireless communication devices 104 dueto the femto access point 106 may be imposed. If the femto access point106 can reduce transmit power and maintain a certain coverage area(i.e., cover as much area as a coverage threshold), then power reductioncan be accomplished. If not, then the femto access point 106 may switchto a different carrier 242.

If power reduction can be accomplished, the vicinity deployment module218 may adjust 306 the transmit power of the femto access point 106 tominimize the impact of the femto access point 106 on the wirelesscommunication devices 104 communicating with the macro base station 102(or other femto access point). Adjusting 306 the transmit power of thefemto access point 106 may include sending an adjusted transmit power tothe femto access point 106 if the vicinity deployment module 218 islocated on the core network 114. The adjusted transmit power may takeinto account the proximity of the femto access point 106 to the macrobase station 102 or other femto access point.

The method 300 of FIG. 3 described above may be performed by varioushardware and/or software component(s) and/or module(s) corresponding tothe means-plus-function blocks 300A illustrated in FIG. 3A. In otherwords, blocks 302 through 306 illustrated in FIG. 3 correspond tomeans-plus-function blocks 302A through 306A illustrated in FIG. 3A.

FIG. 4 is a flow diagram of another method 400 for minimizing theinterference to wireless communication devices 104 near a femto accesspoint 106. The method 400 may be performed by a vicinity deploymentmodule 218. The vicinity deployment module 218 may be located on thefemto access point 106 or on the core network 114. The vicinitydeployment module 218 may determine 402 that a macro base station 102(or other femto access point) with a coverage area overlapping thecoverage area of the femto access point 106 is deployed on an adjacent(or further separated) frequency.

The vicinity deployment module 218 may estimate 404 the amount of radiofrequency (RF) leakage for wireless communication devices 104communicating with the macro base station 102 (or other femto accesspoint) on the adjacent (or further separated) frequency. The amount ofradio frequency (RF) leakage may depend on the current transmit power236 of the femto access point 106, the current carrier of the femtoaccess point 106, the carrier used by the macro base station 102 (orother femto access point) and the adjacent channel interference ratio(ACIR) 238. The femto access point 106 should know the emissions at awide range of carriers. Thus, it can take preventative measures if thereare any carriers with deployments at risk of being affected by the radiofrequency (RF) leakage (i.e., the downlink interference 120).

The vicinity deployment module 218 may determine 406 a different carrier242 than currently used by the femto access point 106 that has less/noadjacent (or further separated) channel deployments. The vicinitydeployment module 218 may switch 408 the femto access point 106 tocommunicating using the determined different carrier 242 with less/noadjacent (or further separated) channel deployments. Switching 408 thefemto access point 106 to the determined different carrier 242 mayinclude sending the determined different carrier 242 to the femto accesspoint 106 if the vicinity deployment module 218 is located on the corenetwork 114.

The method 400 of FIG. 4 described above may be performed by varioushardware and/or software component(s) and/or module(s) corresponding tothe means-plus-function blocks 400A illustrated in FIG. 4A. In otherwords, blocks 402 through 408 illustrated in FIG. 4 correspond tomeans-plus-function blocks 402A through 408A illustrated in FIG. 4A.

FIG. 5 is a timing diagram illustrating a mobile sensing approach tominimizing interference to wireless communication devices 504 near afemto access point 506. A femto access point 506 may broadcast downlinkpilot signals 546. The downlink pilot signals 546 may be received by awireless communication device 504 that is nearby the femto access point506 but not part of the closed subscriber group (CSG) associated withthe femto access point 506. The wireless communication device 504 may bein an active voice call. The wireless communication device 504 maycommunicate with a macro base station 502. Upon receiving the downlinkpilot signals 546, the wireless communication device 504 may detect 548the femto access point 506.

Upon detecting 548 the femto access point 506, the wirelesscommunication device 504 may determine to handoff from the macro basestation 502 to the femto access point 506 during the active call. Tomaintain the active call, the wireless communication device 504 may needto perform an active hand-in to the femto access point 506. In oneconfiguration, the macro base station 502 may instead be another femtoaccess point. The wireless communication device 504 may send a handoffrequest 550 to the macro base station 502. The macro base station 502may forward the handoff request 552 to the core network 514. The corenetwork 514 may be able to control some functions of a femto accesspoint 506.

Information included in the handoff request 552 may not be sufficient touniquely identify the hand-in target. A hand-in target refers to therequested target in a handoff request 552 (i.e., the femto access point506). Upon receiving the handoff request 552, the core network 514 maydetermine 554 a list of possible hand-in targets. The hand-in targets onthe list of hand-in targets may be femto access points that share thesame pseudonoise (PN) code reported by the wireless communication device504 in the Pilot Strength Measurement Message (PSMM) in the handoffrequest 552 along with other supplemental information regarding thevicinity of the wireless communication device 504.

To determine the unique hand-in target, a technique called mobilesensing may be used. In mobile sensing, the core network 514 may send arequest 556 for uplink measurements of the wireless communication device504 (which includes the uplink operating frequency of the wirelesscommunication device 504) to each of the possible hand-in targets. Thefemto access point 506 may receive the request 556 and tune 558 to theuplink operating frequency of the wireless communication device 504. Thefemto access point 506 may then receive uplink pilot signals 560 fromthe wireless communication device 504. The femto access point 506 maycollect 561 uplink pilot signal strength measurements (i.e., energy perchip (Ecp)) over a certain time.

The femto access point 506 may send the uplink pilot signal strengthmeasurements 562 to the core network 514. The core network 514 mayreceive uplink pilot signal strength measurements 562 from multiplefemto access points that were on the list of possible hand-in targets.The core network 514 may then estimate 564 which of the possible hand-intargets is the unique hand-in target (in this case, the femto accesspoint 506). Other techniques for determining the hand-in target may alsobe used, such as additional overhead messages sent by the femto accesspoint 106.

The core network 514 may send a handoff information message 566 to thefemto access point 506. Upon receiving the handoff information message566, the femto access point 506 knows that the wireless communicationdevice 504 is nearby (and that the wireless communication device 504 isnot part of the closed subscriber group (CSG) corresponding to the femtoaccess point 506). In one configuration, the femto access point 506 maydetermine that interference management is necessary based on the outcomeof the mobile sensing. For example, the femto access point 506 maydetermine that interference management is necessary because the mobilesensing indicated that the femto access point 506 was the likely hand-intarget.

Because the femto access point 506 knows the amount of radio frequency(RF) emissions created, the femto access point 506 may take preventativemeasures to create a coverage hole for the wireless communication device504. For example, the femto access point 506 may adjust 568 transmitpower to limit interference. As another example, the femto access point506 may switch 570 carriers to limit interference.

FIG. 6 illustrates the transmission of a handoff request 672 from awireless communication device 604 to a core network 614. The wirelesscommunication device 604 of FIG. 6 may be one configuration of thewireless communication device 104 of FIG. 1. The core network 614 ofFIG. 6 may be one configuration of the core network 114 of FIG. 1. Thewireless communication device 604 may send a handoff request 672 to thecore network 614. Because the wireless communication device 604 cannotcommunicate directly with the core network 614, the wirelesscommunication device 604 may send the handoff request 672 to the corenetwork 614 via a base station (such as a femto access point or a macrobase station 102).

The handoff request 672 may include the downlink pilot signal-to-noiseratio (SNR) 674 of signals received by the wireless communication device604 from the hand-in target. The handoff request 672 may also includethe pseudonoise (PN) code 676 of the detected hand-in target. Due to thehigh reuse of pseudonoise (PN) codes 676 among different femto accesspoints, the information in the handoff request 672 may not be sufficientfor the core network 614 to uniquely identify the hand-in target.Instead, the core network 614 may use mobile sensing to uniquelyidentify the hand-in target. Mobile sensing was discussed above inrelation to FIG. 5 and is discussed in further detail below in relationto FIG. 8.

FIG. 7 is a flow diagram of a method 780 for interference management.The method 780 may be performed by the core network 114. In oneconfiguration, the method 780 may be performed by an apparatus as partof the core network 114. The core network 114 may receive 782 a handoffrequest 672 from a wireless communication device 104. Because thewireless communication device 104 cannot communicate directly with thecore network 114, the handoff request 672 may be received via a basestation (such as a macro base station 102 or a femto access point).

The core network 114 may then determine 784 the femto access point 106that is the hand-in target of the handoff request 672. Determining thata particular femto access point 106 is the hand-in target may be done inmany ways. For example, a mobile sensing approach may be used todetermine that a particular femto access point 106 is the hand-intarget. Mobile sensing is discussed in further detail below in relationto FIG. 8. As another example, additional information sent by the femtoaccess point 106 may be used to identify the femto access point 106 asthe hand-in target. The femto access point 106 may send additionalinformation to the core network 114 in overhead messages that uniquelyidentify the femto access point 106 as the hand-in target. In this case,when a wireless communication device 104 requests a handoff, the corenetwork 114 knows that the handoff request 672 corresponds to the femtoaccess point 106.

The wireless communication device 104 may not be part of a closedsubscriber group (CSG) associated with the femto access point 106.Because the wireless communication device 104 has attempted to handoffto the femto access point 106, the core network 114 may infer that thewireless communication device 104 is nearby the femto access point 106and that the femto access point 106 should enable interferencemanagement.

The core network 114 may send 786 a handoff information message 566 tothe femto access point 106. The handoff information message 566 mayinform the femto access point 106 of the nearby wireless communicationdevice 104 attempting to handoff to the femto access point 106. In oneconfiguration, the handoff information message 566 may inform the femtoaccess point 106 that it is the hand-in target. The handoff informationmessage 566 may also include interference management instructions forthe femto access point 106. For example, the handoff information message566 may include specific instructions for the femto access point 106 toadjust transmit power or switch to a different carrier. In oneconfiguration, the handoff information message 566 may include adictated transmit power for the femto access point 106 to use. Inanother configuration, the handoff information message 566 may include acarrier selected by the network for the femto access point 106 to use.

The method 780 of FIG. 7 described above may be performed by varioushardware and/or software component(s) and/or module(s) corresponding tothe means-plus-function blocks 780A illustrated in FIG. 7A. In otherwords, blocks 782 through 786 illustrated in FIG. 7 correspond tomeans-plus-function blocks 782A through 786A illustrated in FIG. 7A.

FIG. 8 is a flow diagram of a method 700 for mobile sensing. The method700 may be performed by the core network 114. In one configuration, themethod 700 may be performed by an apparatus as part of the core network114. The core network 114 may receive 702 a handoff request 672 from awireless communication device 104. Because the wireless communicationdevice 104 cannot communicate directly with the core network 114, thehandoff request 672 may be received via a base station (such as a macrobase station 102 or a femto access point).

The core network 114 may then determine 704 a list of possible hand-intargets. The list of possible hand-in targets may include femto accesspoints that use the same pseudonoise (PN) code 676 as reported by thewireless communication device 104 in the handoff request 672. Based onthe pseudonoise (PN) code 676 and other supplemental informationregarding the vicinity of the wireless communication device 104, thecore network 114 may determine 704 a reasonably sized list of possiblehand-in targets.

The core network 114 may then request 706 uplink measurements for thewireless communication device 104 from each of the femto access pointson the list of possible hand-in targets. This request may include theuplink operating frequency of the wireless communication device 104 sothat each femto access point can measure the uplink pilot signal of thewireless communication device 104.

The core network 114 may receive 708 uplink measurements for thewireless communication device 104 from each of the femto access pointson the list of possible hand-in targets. Based on the received uplinkmeasurements for the wireless communication device 104, the core network114 may estimate 710 which femto access point is the hand-in target (inthis case, the femto access point 106 is the hand-in target). The corenetwork 114 may then send 712 a handoff information message 566 to thehand-in target. The handoff information message 566 may instruct thefemto access point 106 to adjust transmit power and/or switch carriersto limit interference.

The method 700 of FIG. 8 described above may be performed by varioushardware and/or software component(s) and/or module(s) corresponding tothe means-plus-function blocks 700A illustrated in FIG. 8A. In otherwords, blocks 702 through 712 illustrated in FIG. 8 correspond tomeans-plus-function blocks 702A through 712A illustrated in FIG. 8A.

FIG. 9 is a flow diagram of another method 800 for interferencemanagement. The method 800 may be performed by a femto access point 106.The femto access point 106 may be the hand-in target for a wirelesscommunication device 104. The femto access point 106 may receive 802 arequest for uplink measurements of the wireless communication device 104from the core network 114. As discussed above, the request for uplinkmeasurements of the wireless communication device 104 may include theuplink pilot frequency used by the wireless communication device 104.The femto access point 106 may tune 804 to the uplink pilot frequency ofthe wireless communication device 104.

The femto access point 106 may then receive 806 uplink signals from thewireless communication device 104. For example, the femto access point106 may receive the uplink pilot signal 112 transmitted by the wirelesscommunication device 104. The femto access point 106 may generate 808uplink measurements from the received uplink signals. The femto accesspoint 106 may then send 810 the uplink measurements to the core network114.

Once the core network 114 has identified the femto access point 106 asthe possible hand-in target, the femto access point 106 may receive 812a handoff information message 566 from the core network 114. When thefemto access point 106 receives 812 a handoff information message 566(and has thus been determined to be the hand-in target), the femtoaccess point 106 knows that a nearby wireless communication device 104communicating with a macro base station 102 (or other femto accesspoint) can hear a pilot signal or beacon signal transmitted by the femtoaccess point 106. Given that the wireless communication device 104 isnot allowed to be served by the femto access point 106 (i.e., thewireless communication device 104 is not part of the closed subscribergroup (CSG) associated with the femto access point 106), the femtoaccess point 106 is likely to create a coverage hole for the wirelesscommunication device 104.

The handoff information message 566 may include instructions for thefemto access point 106. For example, the handoff information message 566may instruct the femto access point 106 to adjust 814 the transmit powerof the femto access point 106 to limit interference to the wirelesscommunication device 104. In one configuration, the handoff informationmessage 566 may indicate the adjusted transmit power to be used by thefemto access point 106. In another configuration, the handoffinformation message 566 may only indicate that a change in transmitpower is needed, allowing the femto access point 106 to determine theappropriate power adjustment. As another example, the handoffinformation message 566 may instruct the femto access point 106 toswitch 816 carriers to limit interference to the wireless communicationdevice 104. In one configuration, the handoff information message 566may indicate which different carrier 242 the femto access point 106 isto switch to. In another configuration, the handoff information message566 may only indicate that a switch is necessary, allowing the femtoaccess point 106 to select a different carrier 242.

The method 800 of FIG. 9 described above may be performed by varioushardware and/or software component(s) and/or module(s) corresponding tothe means-plus-function blocks 800A illustrated in FIG. 9A. In otherwords, blocks 802 through 816 illustrated in FIG. 9 correspond tomeans-plus-function blocks 802A through 816A illustrated in FIG. 9A.

FIG. 10 illustrates certain components that may be included within afemto access point 906. A femto access point 906 may also be referred toas, and may include some or all of the functionality of, an accesspoint, a broadcast transmitter, a home evolved NodeB (HeNB), afemtocell, a picocell, etc. The femto access point 906 includes aprocessor 903. The processor 903 may be a general purpose single- ormulti-chip microprocessor (e.g., an ARM), a special purposemicroprocessor (e.g., a digital signal processor (DSP)), amicrocontroller, a programmable gate array, etc. The processor 903 maybe referred to as a central processing unit (CPU). Although just asingle processor 903 is shown in the femto access point 906 of FIG. 10,in an alternative configuration, a combination of processors (e.g., anARM and DSP) could be used.

The femto access point 906 also includes memory 905. The memory 905 maybe any electronic component capable of storing electronic information.The memory 905 may be embodied as random access memory (RAM), read-onlymemory (ROM), magnetic disk storage media, optical storage media, flashmemory devices in RAM, on-board memory included with the processor,EPROM memory, EEPROM memory, registers, and so forth, includingcombinations thereof.

Data 907 and instructions 909 may be stored in the memory 905. Theinstructions 909 may be executable by the processor 903 to implement themethods disclosed herein. Executing the instructions 909 may involve theuse of the data 907 that is stored in the memory 905. When the processor903 executes the instructions 909, various portions of the instructions909 a may be loaded onto the processor 903, and various pieces of data907 a may be loaded onto the processor 903.

The femto access point 906 may also include a transmitter 911 and areceiver 913 to allow transmission and reception of signals to and fromthe femto access point 906. The transmitter 911 and receiver 913 may becollectively referred to as a transceiver 915. An antenna 917 may beelectrically coupled to the transceiver 915. The femto access point 906may also include (not shown) multiple transmitters, multiple receivers,multiple transceivers and/or additional antennas.

The various components of the femto access point 906 may be coupledtogether by one or more buses, which may include a power bus, a controlsignal bus, a status signal bus, a data bus, etc. For the sake ofclarity, the various buses are illustrated in FIG. 10 as a bus system919.

FIG. 11 illustrates certain components that may be included within acore network apparatus 1014. The core network apparatus 1014 may be amachine or machines that provide communication services to a wirelesscommunication network 100. The core network apparatus 1014 includes aprocessor 1003. The processor 1003 may be a general purpose single- ormulti-chip microprocessor (e.g., an ARM), a special purposemicroprocessor (e.g., a digital signal processor (DSP)), amicrocontroller, a programmable gate array, etc. The processor 1003 maybe referred to as a central processing unit (CPU). Although just asingle processor 1003 is shown in the core network apparatus 1014 ofFIG. 11, in an alternative configuration, a combination of processors(e.g., an ARM and DSP) could be used.

The core network apparatus 1014 also includes memory 1005. The memory1005 may be any electronic component capable of storing electronicinformation. The memory 1005 may be embodied as random access memory(RAM), read-only memory (ROM), magnetic disk storage media, opticalstorage media, flash memory devices in RAM, on-board memory includedwith the processor, EPROM memory, EEPROM memory, registers, and soforth, including combinations thereof.

Data 1007 and instructions 1009 may be stored in the memory 1005. Theinstructions 1009 may be executable by the processor 1003 to implementthe methods disclosed herein. Executing the instructions 1009 mayinvolve the use of the data 1007 that is stored in the memory 1005. Whenthe processor 1003 executes the instructions 1009, various portions ofthe instructions 1009 a may be loaded onto the processor 1003, andvarious pieces of data 1007 a may be loaded onto the processor 1003.

The core network apparatus 1014 may also include a transmitter 1011 anda receiver 1013 to allow transmission and reception of signals to andfrom the core network apparatus 1014. The transmitter 1011 and receiver1013 may be collectively referred to as a transceiver 1015. An antenna1017 may be electrically coupled to the transceiver 1015. The corenetwork apparatus 1014 may also include (not shown) multipletransmitters, multiple receivers, multiple transceivers and/oradditional antennas.

The various components of the core network apparatus 1014 may be coupledtogether by one or more buses, which may include a power bus, a controlsignal bus, a status signal bus, a data bus, etc. For the sake ofclarity, the various buses are illustrated in FIG. 11 as a bus system1019.

FIG. 12 illustrates two wireless devices in a multiple-in andmultiple-out (MIMO) system 1180. A first wireless device 1160 may be abase station and a second wireless device may be a wirelesscommunication device. At the first wireless device 1160, traffic datafor a number of data streams is provided from a data source 1162 to atransmit (TX) data processor 1163. Each data stream may then betransmitted over a respective transmit antenna.

The TX data processor 1163 formats, codes and interleaves the trafficdata for each data stream based on a particular coding scheme selectedfor that data stream to provide coded data. The coded data for each datastream may be multiplexed with pilot data using OFDM or other suitabletechniques. The pilot data is typically a known data pattern that isprocessed in a known manner and may be used at the receiver system toestimate the channel response. The multiplexed pilot and coded data foreach data stream is then modulated (i.e., symbol mapped) based on aparticular modulation scheme (e.g., BPSK, QSPK, M-PSK, or M-QAM)selected for that data stream to provide modulation symbols. The datarate, coding and modulation for each data stream may be determined byinstructions performed by a processor 1164. A data memory 1165 may storeprogram code, data and other information used by the processor 1164 orother components of the first wireless device 1160.

The modulation symbols for all data streams are then provided to a TXMIMO processor 1166, which may further process the modulation symbols(e.g., for OFDM). The TX MIMO processor 1166 then provides NT modulationsymbol streams to NT transceivers 1167 a through 1167 t. In someaspects, the TX MIMO processor 1166 applies beam-forming weights to thesymbols of the data streams and to the antenna from which the symbol isbeing transmitted.

Each transceiver 1167 receives and processes a respective symbol streamto provide one or more analog signals, and further conditions (e.g.,amplifies, filters, and upconverts) the analog signals to provide amodulated signal suitable for transmission over the MIMO channel. NTmodulated signals from transceivers 1167 a through 1167 t are thentransmitted from NT antennas 1168 a through 1168 t, respectively.

At the second wireless device 1161, the transmitted modulated signalsare received by NR antennas 1169 a-r and the received signal from eachantenna 1169 is provided to a respective transceiver (XCVR) 1170 a-r.Each transceiver 1170 conditions (e.g., filters, amplifies, anddownconverts) a respective received signal, digitizes the conditionedsignal to provide samples and further processes the samples to provide acorresponding “received” symbol stream.

A receive (RX) data processor 1171 then receives and processes the NRreceived symbol streams from NR transceivers 1170 based on a particularreceiver processing technique to provide NT “detected” symbol streams.The RX data processor 1171 then demodulates, de-interleaves and decodeseach detected symbol stream to recover the traffic data for the datastream. The processing by the RX data processor 1171 is complementary tothat performed by the TX MIMO processor 1166 and the TX data processor1163 at the first wireless device 1160.

A processor 1172 periodically determines which pre-coding matrix to use(discussed below). The processor 1172 formulates a reverse link messagecomprising a matrix index portion and a rank value portion. A datamemory 1173 may store program code, data and other information used bythe processor 1172 or other components of the second wireless device1161. The reverse link message may comprise various types of informationregarding the communication link and/or the received data stream. Thereverse link message is then processed by a TX data processor 1174,which also receives traffic data for a number of data streams from adata source 1175, modulated by a modulator 1176, conditioned by thetransceivers 1170 a-r and transmitted back to the first wireless device1160.

At the first wireless device 1160, the modulated signals from the secondwireless device 1161 are received by the antennas 1166, conditioned bythe transceivers 1167, demodulated by a demodulator (DEMOD) 1177 andprocessed by a RX data processor 1178 to extract the reverse linkmessage transmitted by the second wireless device 1161. The processor1164 then determines which pre-coding matrix to use for determining thebeam-forming weights and then processes the extracted message.

FIG. 12 also illustrates that the communication components may includeone or more components that perform beacon-related operations. Forexample, a beacon control component 1179 may cooperate with theprocessor 1164 and/or other components of the first wireless device 1160to send beacon signals to another device (e.g., the second wirelessdevice 1161) and to receive beacon signals from another device (e.g.,another base station) as taught herein. Similarly, a beacon controlcomponent 1181 may cooperate with the processor 1172 and/or othercomponents of the second wireless device 1161 to receive beacon signalsfrom another device (e.g., the first wireless device 1160). It should beappreciated that for each wireless device 1160, 1161, the functionalityof two or more of the described components may be provided by a singlecomponent. For example, a single processing component may provide thefunctionality of the beacon control component 1179 and the processor1164 and a single processing component may provide the functionality ofthe beacon control component 1181 and the processor 1172.

In some aspects the teachings herein may be employed in a network thatincludes macro scale coverage (e.g., a large area cellular network suchas a 3G networks, typically referred to as a macro cell network) andsmaller scale coverage (e.g., a residence-based or building-basednetwork environment). As an access terminal (“AT”) moves through such anetwork, the access terminal may be served in certain locations byaccess nodes (“ANs”) that provide macro coverage while the accessterminal may be served at other locations by access nodes that providesmaller scale coverage. In some aspects, the smaller coverage nodes maybe used to provide incremental capacity growth, in-building coverage,and different services (e.g., for a more robust user experience). In thediscussion herein, a node that provides coverage over a relatively largearea may be referred to as a macro node. A node that provides coverageover a relatively small area (e.g., a residence) may be referred to as afemto node. A node that provides coverage over an area that is smallerthan a macro area and larger than a femto area may be referred to as apico node (e.g., providing coverage within a commercial building).

A cell associated with a macro node, a femto node, or a pico node may bereferred to as a macro cell, a femto cell, or a pico cell, respectively.In some implementations, each cell may be further associated with (e.g.,divided into) one or more sectors.

In various applications, other terminology may be used to reference amacro node, a femto node, or a pico node. For example, a macro node maybe configured or referred to as an access node, base station, accesspoint, eNodeB, macro cell, and so on. Also, a femto node may beconfigured or referred to as a Home NodeB, Home eNodeB, access pointbase station, femto cell, femto access point, and so on.

FIG. 13 illustrates a wireless communication system 1300, configured tosupport a number of users, in which the teachings herein may beimplemented. The system 1300 provides communication for multiple cells1302, such as, for example, macro cells 1302A-1302G, with each cellbeing serviced by a corresponding access node 1304 (e.g., access nodes1304A-1304G). As shown in FIG. 13, access terminals 1306 (e.g., accessterminals 1306A-1306L) may be dispersed at various locations throughoutthe system over time. Each access terminal 1306 may communicate with oneor more access nodes 1304 on a forward link (“FL”) and/or a reverse link(“RL) at a given moment, depending upon whether the access terminal 1306is active and whether it is in soft handoff, for example. The wirelesscommunication system 1300 may provide service over a large geographicregion. For example, macro cells 1302A-1302G may cover a few blocks in aneighborhood.

FIG. 14 illustrates an exemplary communication system 1400 where one ormore femto nodes are deployed within a network environment.Specifically, the system 1400 includes multiple femto nodes 1410 (e.g.,femto nodes 1410A and 1410B) installed in a relatively small scalenetwork environment (e.g., in one or more user residences 1430). Eachfemto node 1410 may be coupled to a wide area network 1440 (e.g., theInternet) and a mobile operator core network 1450 via a DSL router, acable modem, a wireless link, or other connectivity means (not shown).As will be discussed below, each femto node 1410 may be configured toserve associated access terminals 1420 (e.g., access terminal 1420A)and, optionally, alien access terminals 1420 (e.g., access terminal1420B). In other words, access to femto nodes 1410 may be restrictedwhereby a given access terminal 1420 may be served by a set ofdesignated (e.g., home) femto node(s) 1410 but may not be served by anynon-designated femto nodes 1410 (e.g., a neighbor's femto node 1410).

FIG. 15 illustrates an example of a coverage map 1500 where severaltracking areas 1502 (or routing areas or location areas) are defined,each of which includes several macro coverage areas 1504. Here, areas ofcoverage associated with tracking areas 1502A, 1502B, and 1502C aredelineated by the wide lines and the macro coverage areas 1504 arerepresented by the hexagons. The tracking areas 1502 also include femtocoverage areas 1506. In this example, each of the femto coverage areas1506 (e.g., femto coverage area 1506C) is depicted within a macrocoverage area 1504 (e.g., macro coverage area 1504B). It should beappreciated, however, that a femto coverage area 1506 may not lieentirely within a macro coverage area 1504. In practice, a large numberof femto coverage areas 1506 may be defined with a given tracking area1502 or macro coverage area 1504. Also, one or more pico coverage areas(not shown) may be defined within a given tracking area 1502 or macrocoverage area 1504.

Referring again to FIG. 14, the owner of a femto node 1410 may subscribeto mobile service, such as, for example, 3G mobile service, offeredthrough the mobile operator core network 1450. In addition, an accessterminal 1420 may be capable of operating both in macro environments andin smaller scale (e.g., residential) network environments. In otherwords, depending on the current location of the access terminal 1420,the access terminal 1420 may be served by an access node 1460 of themacro cell mobile network 1450 or by any one of a set of femto nodes1410 (e.g., the femto nodes 1410A and 1410B that reside within acorresponding user residence 1430). For example, when a subscriber isoutside his home, he is served by a standard macro access node (e.g.,node 1460) and when the subscriber is at home, he is served by a femtonode (e.g., node 1410A). Here, it should be appreciated that a femtonode 1420 may be backward compatible with existing access terminals1420.

A femto node 1410 may be deployed on a single frequency or, in thealternative, on multiple frequencies. Depending on the particularconfiguration, the single frequency or one or more of the multiplefrequencies may overlap with one or more frequencies used by a macronode (e.g., node 1460).

In some aspects, an access terminal 1420 may be configured to connect toa preferred femto node (e.g., the home femto node of the access terminal1420) whenever such connectivity is possible. For example, whenever theaccess terminal 1420 is within the user's residence 1430, it may bedesired that the access terminal 1420 communicate only with the homefemto node 1410.

In some aspects, if the access terminal 1420 operates within the macrocellular network 1450 but is not residing on its most preferred network(e.g., as defined in a preferred roaming list), the access terminal 1420may continue to search for the most preferred network (e.g., thepreferred femto node 1410) using a Better System Reselection (“BSR”),which may involve a periodic scanning of available systems to determinewhether better systems are currently available, and subsequent effortsto associate with such preferred systems. With the acquisition entry,the access terminal 1420 may limit the search for specific band andchannel. For example, the search for the most preferred system may berepeated periodically. Upon discovery of a preferred femto node 1410,the access terminal 1420 selects the femto node 1410 for camping withinits coverage area.

A femto node may be restricted in some aspects. For example, a givenfemto node may only provide certain services to certain accessterminals. In deployments with so-called restricted (or closed)association, a given access terminal may only be served by the macrocell mobile network and a defined set of femto nodes (e.g., the femtonodes 1410 that reside within the corresponding user residence 1430). Insome implementations, a node may be restricted to not provide, for atleast one node, at least one of: signaling, data access, registration,paging, or service.

In some aspects, a restricted femto node (which may also be referred toas a Closed Subscriber Group Home NodeB) is one that provides service toa restricted provisioned set of access terminals. This set may betemporarily or permanently extended as necessary. In some aspects, aClosed Subscriber Group (“CSG”) may be defined as the set of accessnodes (e.g., femto nodes) that share a common access control list ofaccess terminals. A channel on which all femto nodes (or all restrictedfemto nodes) in a region operate may be referred to as a femto channel.

Various relationships may thus exist between a given femto node and agiven access terminal. For example, from the perspective of an accessterminal, an open femto node may refer to a femto node with norestricted association. A restricted femto node may refer to a femtonode that is restricted in some manner (e.g., restricted for associationand/or registration). A home femto node may refer to a femto node onwhich the access terminal is authorized to access and operate on. Aguest femto node may refer to a femto node on which an access terminalis temporarily authorized to access or operate on. An alien femto nodemay refer to a femto node on which the access terminal is not authorizedto access or operate on, except for perhaps emergency situations (e.g.,911 calls).

From a restricted femto node perspective, a home access terminal mayrefer to an access terminal that authorized to access the restrictedfemto node. A guest access terminal may refer to an access terminal withtemporary access to the restricted femto node. An alien access terminalmay refer to an access terminal that does not have permission to accessthe restricted femto node, except for perhaps emergency situations, forexample, such as 911 calls (e.g., an access terminal that does not havethe credentials or permission to register with the restricted femtonode).

For convenience, the disclosure herein describes various functionalityin the context of a femto node. It should be appreciated, however, thata pico node may provide the same or similar functionality for a largercoverage area. For example, a pico node may be restricted, a home piconode may be defined for a given access terminal, and so on.

The techniques described herein may be used for various communicationsystems, including communication systems that are based on an orthogonalmultiplexing scheme. Examples of such communication systems includeOrthogonal Frequency Division Multiple Access (OFDMA) systems,Single-Carrier Frequency Division Multiple Access (SC-FDMA) systems, andso forth. An OFDMA system utilizes orthogonal frequency divisionmultiplexing (OFDM), which is a modulation technique that partitions theoverall system bandwidth into multiple orthogonal sub-carriers. Thesesub-carriers may also be called tones, bins, etc. With OFDM, eachsub-carrier may be independently modulated with data. An SC-FDMA systemmay utilize interleaved FDMA (IFDMA) to transmit on sub-carriers thatare distributed across the system bandwidth, localized FDMA (LFDMA) totransmit on a block of adjacent sub-carriers, or enhanced FDMA (EFDMA)to transmit on multiple blocks of adjacent sub-carriers. In general,modulation symbols are sent in the frequency domain with OFDM and in thetime domain with SC-FDMA.

The term “determining” encompasses a wide variety of actions and,therefore, “determining” can include calculating, computing, processing,deriving, investigating, looking up (e.g., looking up in a table, adatabase or another data structure), ascertaining and the like. Also,“determining” can include receiving (e.g., receiving information),accessing (e.g., accessing data in a memory) and the like. Also,“determining” can include resolving, selecting, choosing, establishingand the like.

The phrase “based on” does not mean “based only on,” unless expresslyspecified otherwise. In other words, the phrase “based on” describesboth “based only on” and “based at least on.”

The term “processor” should be interpreted broadly to encompass ageneral purpose processor, a central processing unit (CPU), amicroprocessor, a digital signal processor (DSP), a controller, amicrocontroller, a state machine, and so forth. Under somecircumstances, a “processor” may refer to an application specificintegrated circuit (ASIC), a programmable logic device (PLD), a fieldprogrammable gate array (FPGA), etc. The term “processor” may refer to acombination of processing devices, e.g., a combination of a DSP and amicroprocessor, a plurality of microprocessors, one or moremicroprocessors in conjunction with a DSP core, or any other suchconfiguration.

The term “memory” should be interpreted broadly to encompass anyelectronic component capable of storing electronic information. The termmemory may refer to various types of processor-readable media such asrandom access memory (RAM), read-only memory (ROM), non-volatile randomaccess memory (NVRAM), programmable read-only memory (PROM), erasableprogrammable read-only memory (EPROM), electrically erasable PROM(EEPROM), flash memory, magnetic or optical data storage, registers,etc. Memory is said to be in electronic communication with a processorif the processor can read information from and/or write information tothe memory. Memory that is integral to a processor is in electroniccommunication with the processor.

The terms “instructions” and “code” should be interpreted broadly toinclude any type of computer-readable statement(s). For example, theterms “instructions” and “code” may refer to one or more programs,routines, sub-routines, functions, procedures, etc. “Instructions” and“code” may comprise a single computer-readable statement or manycomputer-readable statements.

The functions described herein may be implemented in software orfirmware being executed by hardware. The functions may be stored as oneor more instructions on a computer-readable medium. The terms“computer-readable medium” or “computer-program product” refers to anytangible storage medium that can be accessed by a computer or aprocessor. By way of example, and not limitation, a computer-readablemedium may comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage or other magnetic storage devices, or anyother medium that can be used to carry or store desired program code inthe form of instructions or data structures and that can be accessed bya computer. Disk and disc, as used herein, includes compact disc (CD),laser disc, optical disc, digital versatile disc (DVD), floppy disk andBlu-ray® disc where disks usually reproduce data magnetically, whilediscs reproduce data optically with lasers.

The methods disclosed herein comprise one or more steps or actions forachieving the described method. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isrequired for proper operation of the method that is being described, theorder and/or use of specific steps and/or actions may be modifiedwithout departing from the scope of the claims.

Further, it should be appreciated that modules and/or other appropriatemeans for performing the methods and techniques described herein, suchas those illustrated by FIGS. 3-4 and 7-9, can be downloaded and/orotherwise obtained by a device. For example, a device may be coupled toa server to facilitate the transfer of means for performing the methodsdescribed herein. Alternatively, various methods described herein can beprovided via a storage means (e.g., random access memory (RAM),read-only memory (ROM), a physical storage medium such as a compact disc(CD) or floppy disk, etc.), such that a device may obtain the variousmethods upon coupling or providing the storage means to the device.

It is to be understood that the claims are not limited to the preciseconfiguration and components illustrated above. Various modifications,changes and variations may be made in the arrangement, operation anddetails of the systems, methods, and apparatus described herein withoutdeparting from the scope of the claims.

What is claimed is:
 1. A method for reducing interference to wirelesscommunication devices, comprising: determining that a base station isdeployed with a first coverage area that overlaps a second coverage areaof a femto access point, wherein the base station uses a first carrierfor wireless communications, wherein the femto access point uses asecond carrier for wireless communications, and wherein transmissions bythe femto access point interfere with transmissions by the base station;receiving a hand-off request from a wireless communication deviceindicating a hand-off attempt to the femto access point; estimating anamount of radio frequency (RF) leakage experienced by wirelesscommunication devices communicating with the base station; andminimizing interference experienced by the wireless communicationdevices based at least in part on the estimated RF leakage, in responseto receiving the hand-off request, by switching the femto access pointto communicating using a third carrier.
 2. The method of claim 1,wherein the method is performed by the femto access point.
 3. The methodof claim 1, wherein the method is performed by a core network apparatus.4. The method of claim 1, wherein the base station is a femto accesspoint.
 5. The method of claim 1, wherein the base station is a macrobase station.
 6. The method of claim 1, wherein determining that thebase station is deployed comprises monitoring a downlink signal strengthon the first carrier.
 7. The method of claim 1, further comprisingdetermining a third carrier different from the first carrier and thesecond carrier.
 8. The method of claim 7, wherein the third carrier hasfewer base station and femto access point deployments than the secondcarrier.
 9. The method of claim 7, wherein the third carrier has no basestation or femto access point deployments.
 10. The method of claim 1,wherein the first carrier and the second carrier are the same carrier.11. The method of claim 1, wherein the first carrier and the secondcarrier are adjacent.
 12. The method of claim 7, wherein the method isperformed by a core network, and wherein switching the femto accesspoint to communicating using the third carrier comprises sending thethird carrier to the femto access point.
 13. The method of claim 1,wherein estimating the amount of RF leakage is performed using a currenttransmit power of the femto access point, the second carrier used by thefemto access point, the first carrier used by the base station and anadjacent channel interference ratio (ACIR).
 14. A wireless deviceconfigured for reducing interference to wireless communication devices,comprising: a processor; memory in electronic communication with theprocessor; instructions stored in the memory, the instructions beingexecutable by the processor to: determine that a base station isdeployed with a first coverage area that overlaps a second coverage areaof a femto access point, wherein the base station uses a first carrierfor wireless communications, wherein the femto access point uses asecond carrier for wireless communications, and wherein transmissions bythe femto access point interfere with transmissions by the base station;receive a hand-off request from a wireless communication deviceindicating a hand-off attempt to the femto access point; estimate anamount of radio frequency (RF) leakage experienced by wirelesscommunication devices communicating with the base station; and minimizeinterference experienced by the wireless communication devices based atleast in part on the estimated RF leakage, in response to receiving thehand-off request, by switching the femto access point to communicatingusing a third carrier.
 15. The wireless device of claim 14, wherein thewireless device is the femto access point.
 16. The wireless device ofclaim 14, wherein the wireless device is a core network apparatus. 17.The wireless device of claim 14, wherein the base station is a femtoaccess point.
 18. The wireless device of claim 14, wherein the basestation is a macro base station.
 19. The wireless device of claim 14,wherein determining that the base station is deployed comprisesmonitoring a downlink signal strength on the first carrier.
 20. Thewireless device of claim 14, wherein the instructions are furtherexecutable to determine a third carrier different from the first carrierand the second carrier.
 21. The wireless device of claim 20, wherein thethird carrier has fewer base station and femto access point deploymentsthan the second carrier.
 22. The wireless device of claim 20, whereinthe third carrier has no base station or femto access point deployments.23. The wireless device of claim 14, wherein the first carrier and thesecond carrier are the same carrier.
 24. The wireless device of claim14, wherein the first carrier and the second carrier are adjacent. 25.The wireless device of claim 20, wherein the wireless device is a corenetwork apparatus, and wherein switching the femto access point tocommunicating using the third carrier comprises sending the thirdcarrier to the femto access point.
 26. The wireless device of claim 14,wherein estimating the amount of RF leakage is performed using a currenttransmit power of the femto access point, the second carrier used by thefemto access point, the first carrier used by the base station and anadjacent channel interference ratio (ACIR).
 27. A wireless deviceconfigured for reducing interference to wireless communication devices,comprising: means for determining that a base station is deployed with afirst coverage area that overlaps a second coverage area of a femtoaccess point, wherein the base station uses a first carrier for wirelesscommunications, wherein the femto access point uses a second carrier forwireless communications, and wherein transmissions by the femto accesspoint interfere with transmissions by the base station; means forreceiving a hand-off request from a wireless communication deviceindicating a hand-off attempt to the femto access point; means forestimating an amount of radio frequency (RF) leakage experienced bywireless communication devices communicating with the base station; andmeans for minimizing interference experienced by the wirelesscommunication devices based at least in part on the estimated RFleakage, in response to receiving the hand-off request, by switching thefemto access point to communicating using a third carrier.
 28. Acomputer-program product for reducing interference to wirelesscommunication devices, the computer-program product comprising acomputer-readable medium having instructions thereon, the instructionscomprising: code for causing at least one computer to determine that abase station is deployed with a first coverage area that overlaps asecond coverage area of a femto access point, wherein the base stationuses a first carrier for wireless communications, wherein the femtoaccess point uses a second carrier for wireless communications, andwherein transmissions by the femto access point interfere withtransmissions by the base station; code for receiving a hand-off requestfrom a wireless communication device indicating a hand-off attempt tothe femto access point; code for causing at least one computer toestimate an amount of radio frequency (RF) leakage experienced bywireless communication devices communicating with the base station; andcode for causing at least one computer to minimize interferenceexperienced by the wireless communication devices based at least in parton the estimated RF leakage, in response to receiving the hand-offrequest, by switching the femto access point to communicating using athird carrier.
 29. The method of claim 1, wherein the femto access pointis configured to provide coverage over an area smaller than a picocell.